Rectifier



April 2, 1929. e. B. C'QLEMAN 1,707,936

RECTIFIER I Filed Nov. 22. 1922 2 Sheets-Sheet 1 FIELI.

FIELE.

3/ Q 01 I 1 P/l INVENTOR. I Ci 3. Coleman WITNE$5 Q J2 iva/ ATTORNEYS.

April 2, 1929. G. B. COLEMAN 1,707,936

RECTIFIER Filed Nov. 22. 1922 2 Sheets-Sheet 2 FIELEI.

IN VEN TOR. G. 5. Co/e'rnan 4 A TTORNEYS.

. of use with such inefficient Patented Apr. 2, 1929.

UNITED STATES PATENT orrics.

GEORGE B. CQLEMAN, SAN FRANCISCO, 'OALIFORHIA, ASSIGNOB, BY DIRECT AND MESNE ASSIGNMENTS, OFONE-FOUBTH TO SAID COLEMAN, ONE-FOURTH TO PAUL J'. BOYENS, AND ONE-FOURTH TO CHARLES- CALIFORNIA, AND 0NE-FOURTH T0 LELAIITDv E. CARTER.

a. MCCARTHY, ALL or sen FRANCISCO,

RECTIFIER.

Application filed November 22, 1922.

Thi invention relates to a rectifier, or switching means for electric current, and more particularly to such a rectifier capable devices as X-ray tubes, storage batteries, or the like. V

The most'difiicult problems encountered with such mechanical rectifiers whenused for high tension work, are to keep the currentcarrying parts sufficiently well insulated,and also to prevent undue sparking at the'con- ;tacts. In general, it is one of the objects of my invention to attain these results.

In X-ray systems especially, where voltages ofthe order of'100,000 are used, these problems become acute. Cumbersome and expensive apparatus has been proposed for this purpose, but they have obvious disadvantages. For example, in order to avoid excessive sparking, it has beencustomary to utilize aspecially constructedhigh voltage transformer between the source and the rectifier which transformer is supposed to minimize the sparking at the instant the circuit is broken at the rectifier switch. In order the-tit may accomplish this result, a highly transformer results, there being of necessity a very large energy loss in the coils of the transformer. It is another ob .ject of my invention to provide a rectifier free from excessive sparking and so arranged that no special transformer or source need be used therewith.

These highly important results I am capable of attaining by the use ofa compound .rectifienelements of which are disposed in series so as to interrupt and to reverseat a plurality of points in seriesfthe circuit of the alternating current source. The first and lastpoints may thus be separated byas great a distance as is necessary, without theaid of large sized rotating switches. Since the circuit is broken at many places simultaneously, the tendency to generate injurious sparking atany one place is overcome. I

While the simplest form of my invention is that in} which but one half of each alternating current cycle is utilized, it is not limited to that form. By appropriate combinations of series switches it is possible to rectify both half waves, or any portions of them, while theadvantages of obviating in urious sparking and of maintaining higlji insulation my invention four switches are Serial No. 602,597.

are still present. It is thus another object of my invention to provide a full wave rectifier utilizing switches in series of simple and inexpensive construction and having desirable operating characteristics. i Myinvention possesses other advantageous features, some of which, will be set forth at length in the following description, where I shall outline in full those forms of the invention that I have selected for illustrat'ionin the drawings accompanying and forming part of the present specification. Although I have shown but a few embodiments of my invention in the drawings, it is'to be understood that I do not wish to be limited thereto, since the invention as expressed in the claims may be-embodied-in other forms also.

Referring to the drawings: Figure 1 is a side view of a rectifier embodying my'invention, in which. half wave rectification only is obtained; 'Fig. 2 is an end view of the rectifier shown in Fig. 1, with theend bearing removed for the sake of clearnes's; Yr

ig. 3 is a wiring diagram illustrating my invention applied to an X-ray system; i Fig. 4k is a view, mainly diagrammatic, of a rectifier for both Fig.6 is a diagrammatic view of still another form of my invention, in which both half-waves are also rectified; and

F ig.'6 is a side elevation of a transformer structure with a rectifier, illustrating-in a diagrammatic manner how these two elements 'may be compactly assembled.

In the embodiment shown in Figs. land 2, only one-half of each cycle, or less, is rectified in other words, during the remainder of the cycle the circuitfrom the alternating current source to the translating device is interrupted. This is effected by a plurality of rotary switches or commutators arranged on a common shaft 11. journaled in the end bearings 12 resting on a supporting base 13, and is adapted to be rotated at a speed exactly proportional to the frequency of the current to be'rectified, as

by the aid of a small electric motor 14 of a synchronous type. In the present instance shown, but of course there with the foregoing,

half-wav.%, embodying This shaft is appropriately may be more or less, depending upon the conditions of operation. One of the switches is most clearly shown in the end view of Fig. 2, wherein one element of the switch is shown as a rotatable electrode or brush 15, in the form of a metallic rod. This brush or electrode is arranged to cooperate with the stationary part of the switch, which includes a pair of arcuate conducting segments 16 and 17, placed so as to be bridged periodically by the rod or brush 15. These segments 16 and 17 may be arranged to subtcnd any required angle, so that the circuit through the switch from. segment to segment may be completed for any desired portion only of a cycle. In orderto maintain this circuit properly isolated, that portion of shaft 11 through which the electrode or brush 15 passes is made of insulating material, although at the ends where the shaft is journaled, I prefer it to be formed of metal. Of course other arrangements for insulating the rotating brush 15 may be used.

The segment 16 forms one terminal of the rectifier and for this purpose it is appropriately supported in its position in a clamp block 18 of insulating material, appropriately supported on base 13. For convenience the segment 16 may be formed from a round copper rod or bar, having an upstanding portion 19 to which the incoming wires may be attached, and which is securely clamped in position by the block 18.

In the present instance no rubbing contact is provided from segments 16, 17 to electrode 1.); instead a small arc is formed between these .parts. This feature is not objectionable where exceptionally high voltages and small currents arerectitied, since no material loss in voltage is then suffered by forcing the minute current across the air gap.

Succeeding switches 20, 21 and 22 entirely similar to that just described, are placed axially along the shaft 11, and all the switches are placed in series relation. This may be effected by the aid of appropriate conductors, but for the sake of convenience, I prefer to form the connecting conductor from one switch to another integral with the segments with which the conductor is associated. Thus segment 17 is connected to a segment 23 of switch by a bowed or arched inte ral portion 24-. Clamps 18 form supports for these bowed portions, in a manner entirely similar to that for the end segment 16. Similar bowed connections 25 and 26 serve to place the remaining two switches 21 and 22 in series, and the end segment of the last switch 22 forms the other terminal of the rectifier. Each of the switches also has a rotating electrode 27, 28 or 29 similar to electrode 15 for the first switch, and arranged in such a way that as shaft 11 is rotated, all of them leave and approach their segments simultaneously and in phase. It is thus seen that the current entering through either one or the other of the end terminals, must pass switches in. series before it out at the other terminal.

This latter feature is most clearly illustrated in Fig. 3, wherein the segments 16 and 30 form the terminals of the rectilier. A source of alternating current, such as a sec ondary winding 31 of a high potential trans former, is connected in series with a translating device, sucl as an X-ray tube 32, and with the rectifier. Twice during one revolution of the shaft 11., current may fiow through the tube 32 for a period dependent upon the angle subtended by the segments. The spced of the shaft is synchronous and of such a value that these connect ions are effective for a portion of a half-cycle, and are open for the remainder of the cycle. Thus with this form of rectilier (usually called a half-wave rectifier) current is permitted to flow only when the polarities of the transformer terminals have a predetermined relation. Sui-a a device may be used, not only for X-ray work, but also for smoke precipitation or the like.

The important advantages that may be secured by the form of construction illustrated, are numerous. Thus it is possible to separate the terminals of the rectifier by as great a distance as desired, without the aid of cumbersome large diameter rotating elements. Furthermore breaking the current at a plurality of points reduces arcing materially; this feature is especially important in low tension, large current rectitiers, in battery chargers, where the heavy current would otherwise seriously injure the elec trodes every time the circuit is interrupted. A plurality of switches in series as described serves to reduce the voltage per contact and the injurious arcing is prevented. Thus with eight contacts as shown in the embodimci'lt of Fig. 1, the volts per contact are but one eighth of the total voltage of the arc.

Although I have shown all of the switches of the compound rectifier mounted one behind the other along a common shaft 11, it is of course possible to arrange them along a plurality of shafts, each synclu'ontmsly driven or else geared together. Such an arrangement may be especially useful where many switch elements must be placed in series, for then mechanical difficulties may arise in connection with the proper support for the shaft.

It is possible to extend the principle of the invention so as to rectify both half-waves of the alternating current cycle. Such a rectilier is illustrated diagrammatically in i l. In this case the transformer sccomlary winding 33 is connected so that it has alternate, parallel paths through the rectifier. Thus its top terminal 34; is joined to two sets of series switches and 36. These switches are substantially similar to those already through all the "an find its way the stationary brushes decribed, but in the present instance they are illustrated with actualcontact between 37 and the rotating segments 38.

' The set of switches 35 is arranged to have their circuits complete substantially for one entire half-cycle, while the other set 36 is arranged to have their circuits complete substantially for the other half-cycle. Thus the rotating segments for the two sets of switches are -angularly displaced on the shaft 139 to the proper extent to effect this result. A

' small synchronous motor 40 may, as before,

serve to supply the motive power for the rectifier.

The lower terminal 41 of the winding 33 is similarly connected to two 'setsof switches 42 and 43 entirely similar to the sets 35 and 36, and also arrangedin parallel. Thus the four sets of switches serve as reversing switches for the terminals 34 and 41. l Vhile the current in the transformer winding is in the direction indicated by thearrow 44 drawn in full lines, the current may flow from the left hand terminal 45 of the set of switches 42, through these switches, through connection 46, lowerterminal 41, winding 33, upper terminal 34, set of switches 35, to a terminal 47. Now if a translating device, such as an X-ray tube 48, be connected to terminals 45 and 47, currentv will flow through it periodically in the path just traced, in the direct-ion shown by the arrows 49 and 50.

For the succeeding half-cycle the current flow in the transformer coil 33 is in the direction shown by the arrow 51 drawn in dotted lines. At the same time, the sets of switches 35 and 42 are open, while sets 36 and 43 are closed, and the current can now flow from the lower terminal 41, connection 46, switches 43, through tube 48, switches 36, and upper terminal 34 back to the winding 33. It is thus seen that both half-waves of current are rectified, even while the advantages of the first form of apparatus described, are retained. Thus there is as great a separation between the terminals of the various sets of switches as desired, without resorting to cumbersome rotating elements, and furthermore the'circuit is broken at as many points in series as desired. By properly proportioning the various switch parts, it is possible to make use of as much of each halfwave of current as desired; it is usually advantageous to use substantially the whole cycle, for then the translating device is sup plied with the maximum energy per cycle. This maximum use of the half cycles is usually more diflicult of attainment in other types of rectifiers, due to the fact that the opposite poles of such devices approach objectionably near to each other if itbe attempted to extend the current carrying parts so as to render the rectifier active for a major tion; that is, only terminal of the translating a complete half-cycle.

portion of the cycle. It is evidentthat no such difficulty is met with in the apparatus described.

In order to render the device capable of use as a half wave rectifier, an appropriately po- 'sitioned switch 52 may be used, which, when opened, renders two of the four sets of switches 35, 36, 42 and 43 inactive. In the location shown, switch 52 renders switches 35 and 42 inactive, and current can flow only wli'enswitches 36 and 43 are in closed posiwhen the current in transformer winding 33 can flow in the direction of the arrow 51.

v A somewhat simplified form of full wave rectifier embodying my invention is illustrated diagrammatically in Fig. 5. In this case only half of the transformer winding 53 is active at any time, and there is a connection at the central point 54 directly to one device, shown in this instance'as a storage battery 55, which is to be charged. The other terminal of the battery connects betweenthe two series of switches 56 and57, through small inductan ces 69 and 70, while the terminals of the coil 53 are connected to the free ends of the switches. In the position shown, current may flow as shown by the full line arrow 58 through switches 56 and inductances 69 to battery 55 backto the central connection 54. In the succeeding half-cycle, if the switch be closed, current may flow as shown by the dotted line to battery 55, back to the central point 54. Since in battery charging systems such as shown in this form, it is advantageous not to leave the battery circuit open at all, the switches 56 and 57 are made to rectify each The inductances 69 and 70 prevent short-circuiting of the transformer winding at the instant the connections are changed from one set of switches to the other, and also help in a measure to smooth out the rectified current.

Another important advantage arising from c the construction described is the simple manner in which the entire rectifier may be assembled with a transformer. Thus in Fig. 6, the rectifier 60 is shown as mounted with its axis vertical upon'the transformer casing 61,

and is shown as encased in a hollow insulating tube 62. Although that form of the rectifier is shown which has been described in connection with Fig. 4, it is evident that any of the other forms may also be supported in this way. The various connectionsto the transformer and the translating device may be provided for by heavily insulated cables or wires which connect with conducting members extending through the walls of the. tube 62. Thus the terminals 65 and 66 of the transformer secondary are appropriately connected to the rectifier 60 by the aid of leads 63 and 64, while the translating device may be connected to the rectifier by the aid of leads G7 and 68. Preferably the rectifier is placed between the two terminal posts of the transformer. Its position on top of the casing 61 places it out of reach of accidental contact, and also assists in keeping the device free from disturbing influences.

Al though I have shown my invention as applied to a mechanical rectifier, it is obvious that means other than mechanical may be employed to interrupt the current, such as valve tubes, chemical or other means of interrupting electric current. It is understood that a number of changes or modifications as to the details of my invention might be made without altecting the spirit of the invention and without leaving the scope of the claims hereto attached.

I claim:

1. An alternating current rectifier comprising a plu'ality of switch members oi which each con'iprises spaced areuate segments and a brush substantially spanning the distance between the segn'ients, connectors electrically connecting certain oi: the segments of adjacent switches, and a brush actuator consisting of a shaft concentric with the segments of the several switches and means tor driving the same in synchronism with the periodicity of the current to be rec tified, the connectors between adjacent switches consisting of bowed elements spanning the shaft and extending from. the segment o't one switch to the segn'ient of an adjacent switch on the opposite side of the shaft.

2. An alternating current rectifier comprising a shaft, means for driving the same in synchronism with the periodicity oi the current to be rectified, bearings for said shaft, and a plurality of switches of which each comprises a pair of supports arranged on opposite sides ot the shaft, arcuat'e segments concentric with the shaft and secured one to each of said supports, and bowed connectors extending over the shaft and electrically connecting a segment of each switch with the segment oi? an adjacent switch disposed on the opposite side of the shaft.

In testimony whereof, I have hereunto set my hand.

GEORGE B. COLEMAN. 

